The present invention relates to an object confirming apparatus which can detect the presence or location of an object by trasmitting pulses of ultrasonic waves periodically and detecting the reflected back waves of the pulses from the object in order to confirm the presence or location thereof or if necessary to obtain the distance from the object.
Sonars or ultrasonic radars have widely been used for detecting the presence or location of an object or obtaining the distance from the object, and in these apparatuses consideration has been given to removing objectionable noise.
Hereinafter the examples and principles of such conventional apparatuses will be briefly explained using FIGS. 1 and 2, FIG. 1 being a block diagram showing such a conventional apparatus and FIG. 2 being a waveform diagram for explaining the operation of the apparatus of FIG. 1. The time interval, or period, at which the ultrasonic waves are transmitted is determined by a time base generator 1. In FIG. 2(a), a pulse train for a basic period Ts is shown. By this pulse train, a transmitter pulse generator 2 is actuated which determines the pulse width, and during this pulse width an ultrasonic frequency oscillator 3 is operated. The output of the oscillator 3 is power amplified by a power amplifier 4, and the output of the amplifier drives a transmitting transducer 5 for transmitting ultrasonic waves.
The ultrasonic waves are thus transmitted by the transducer 5 into space and reflected from an object after they hit against the object. These reflected ultrasonic waves are received by a receiving transducer 6. The output from the transducer 6 is amplified by an amplifier 7 which is tuned to the frequency of the ultrasonic waves transmitted. The tuned amplifier 7 is used for removing noise components at other frequencies. The output of the amplifier 7 is converted into pulses through a receiving pulse generator 8, which limits ouptut signals exceeding a predetermined level to that of the level so as to remove noise components of a lower level. The time interval t.sub.R1 (see FIG. 2) from the generation of the output pulses from the time base generator 1 until the output from the pulse generator 8 is outputted is in proportion to the distance from the object, and therefore the distance may be indicated by an indicator 10, taking the interval t.sub.R1 as the integrating time of an integrating circuit 9.
Thus care has been taken to remove noise in these apparatuses as shown above. On the other hand, the present invention is directed to locating and selecting a correct signal, more than to the removal of noise. Particular attention was paid to the periodicity of the signal components for the purpose of confirmation. As is shown in FIG. 2, assuming that the object is static with respect to the fixed transducers 5 and 6 (see FIG. 1), the time interval t.sub.R1 from the time of trasmission of the first wave (t.sub.o) and receipt of the reflected wave is the same as t.sub.R2 for the second transmission t.sub.1. The receiving period T.sub.R is equal to T.sub.s.
In Japanese laid open patent application No. 11535/1977, titled "Monitor for the Rear of Automobile", there is shown a circuit utilizing the periodicity. In this circuit, after detecting one reflected wave, masking is effected for a time shorter than the whole period to remove noise and to obtain the correct next reflected wave. This is advantageous with respect to the removal of noise.